Contemporary wireless communication systems are characterized by multiple radio access technologies, some of which result from an evolution of successive generations of cellular communications services and some of which represent wireless communication services that have developed outside the conventional cellular paradigm. Examples of the former include Universal Mobile Telecommunications System (UMTS) and Long Term Evolution (LTE), while 802.11 services such as Wi-Fi exemplify the latter. A multi-mode user terminal (hereafter usually referred to as a mobile node) having RF capabilities compatible with two or more radio access technologies can switch to an available technology that is most suitable at the relevant time. This provides advantages for both the user—who may be able to access a network operating with a given technology at a given time, but not a network for the other technology supported by the user's terminal, and the system operator operating with multiple technologies in its network—which will often be able to do load-sharing between different technology carriers, so as to improve network usage and performance.
At least for the case of user terminals supporting access with both a conventional cellular system and with an 802.11 system, the aggregate available network may be characterized as implementing a hybrid cellular architecture. An advantage of hybrid cellular architectures lies in the ability of end-user devices to assist the base station (BS) in various functions by acting as content caches, cell relays, aggregators, mobility predictors, and the like. In a hybrid architecture, the key differentiator is that the base station knows the location of a given mobile node (MN) as well as that of its neighbors. This location information supports the determination by the base station of the topology of a network formed by the mobile nodes using their secondary radio (generally, the radio supporting access to an 802.11 system). Availability of this topology information is vital for the base station in order to fully exploit the potential benefits of a hybrid architecture.
Although procedures for discovery of topology information by mobile nodes in a cell is generally known in the art, the conventional focus has been on how each node discovers the entire network connectivity graph. In a hybrid model, the base station has to know the topology of the underlying network graph among its served MNs. However, the base station does not necessarily need to know the entire set of links among all of the served MNs. For example, the base station might be interested in knowing only the high-quality links between the served MNs, or it might be interested in knowing only if there exists at least one path between those MNs, etc. Many of these functions may be addressed without knowledge of the entire topology of the MN network. The reduced topology so needed is referred to herein as a compact topology graph (CTG).
Another issue is that, while topology discovery can happen in a distributed manner for an ad-hoc wireless network, in the case of a hybrid network, the process is centralized in nature with all mobile nodes informing a single destination (i.e., base station) about their neighbors. This can result in excessive transmission overhead.
In modern cellular data networks, communication from the MN to the base station involves some signaling to acquire a bearer channel and once the bearer is acquired, transmission of data over the bearer. For a typical cell with hundreds of users, doing the above solely for the purpose of topology discovery can become a significant bottleneck.
A typical manner in which this resource constraint can be relaxed is by use of clustering, wherein groups of MNs organize themselves into clusters and elect a cluster-head (CH), with each CH discovering the cluster topology and communicating this to the base station. Thus, the signaling overhead is proportional to the number of CHs, while the data transmitted is at most the same as before. In principle, each CH performs at least one of the functions: (a) identify the membership information for each cluster, or (b) identify the topology of the cluster. However, the methods of the art carry out such functions in a sub-optimal way.